The present invention relates to a method of and to an apparatus for inserting radially expandible inner tubes into outer tubes. More particularly, the invention relates to improvements in a method and apparatus for inserting radially expandible inner tubes which consist of convoluted or otherwise deformed sheet-like material into normally rigid or substantially rigid outer tubes. Typical examples of inner tubes which can be formed and manipulated in accordance with the method and in the apparatus of the present invention are rolled or otherwise shaped sheets of synthetic plastic separator material which are confined in tubular bodies consisting of carbon or the like and are disposed in the interior of metallic housings or shells (also called cans) of cylindrical alkaline batteries, especially so-called dry cells.
A problem which arises in connection with the mass-production of rod-shaped dry cells is that of predictably inserting inner tubes of synthetic plastic separator material into outer tubes in such a way that the inner tubes are free, or are compelled, to expand into intimate contact with the internal surfaces of the respective outer tubes. The insertion of each inner tube must be completed within a small fraction of one second, and each inner tube should contact the internal surface of the respective outer tube even if the inner diameter of the outer tube (e.g., a hollow cylinder made of carbon) deviates from a standard value. Moreover, the smoothness of the internal surfaces of outer tubes often fluctuates within a wide range and the inner tubes are likely to be formed with internal protuberances which interfere with predictable insertion of inner tubes.
Certain presently known proposals to make inner tubes include placing two strips of deformable sheet material across each other to form a cruciform blank and thereupon forcing the central portion of the blank (namely the portion where the two strips overlap each other) into a cylindrical socket so that the blank is converted into an inner tube one end of which is closed and which is ready for insertion into an outer tube. A drawback of such inner tubes is that their thickness is not constant, as considered in the circumferential direction, as well as that the making of cruciform blanks is a time-consuming operation.
Another prior proposal involves the making of inner tubes by rolling flexible sheets into cylinders and by thereupon upsetting one end portion of each cylinder to form an elongated basket one end of which is closed. The basket is then ready to be inserted into an outer tube. This proposal exhibits the drawback that the basket cannot expand along its full length and also that the making of baskets takes up relatively long intervals of time.
A further prior proposal includes the utilization of adhesive to bond the layers of rolled sheets to each other. The adhesive prevents expansion of inner tubes into extensive contact with the outer tubes.
It was also proposed to use cylindrical inner tubes of rolled sheet material and to insert into each inner tube a separately produced cup which is adhesively secured to one end portion of the inner tube. The outermost convolution of each inner tube is bonded to the adjacent convolution. The cost of such inner tubes is very high, primarily due to lack of adequate apparatus for converting sheets of separator material into inner tubes.
Reference may also be had to commonly owned British Pat. No. 1,556,154 to Schubert et al.